chore(docs): agents context file

AGENTS.md

@@ -1,10 +1,84 @@
-# AI Agent Guidelines
+# Filecoin Pin
 
-When using AI agents (such as Claude Code, Cursor, or similar tools) to contribute to this project, please ensure the agent follows all guidelines outlined in [CONTRIBUTING.md](./CONTRIBUTING.md).
+IPFS persistence layer for Filecoin with verifiable storage proofs. TypeScript library + CLI + GitHub Action.
 
-This includes:
-- Using conventional commits
-- Referencing GitHub issues in PRs
-- Including visual evidence for user-facing changes
-- Keeping PRs in draft until ready for review
-- Writing concise, self-documenting code
+## What This Is
+
+Bridges IPFS content to Filecoin storage providers with cryptographic guarantees. Production tool + reference implementation for building on synapse-sdk.
+
+**Affordances**: CLI (`add`, `payments`, `data-set`), GitHub Action, core library (published npm modules), IPFS Pinning Server (`server` daemon).
+
+**Stack**: filecoin-pin → synapse-sdk → FOC contracts (FWSS, FilecoinPay, PDPVerifier, SPRegistry) + Curio.
+
+**Status**: Calibration testnet only. Not production-ready.
+
+## Architecture
+
+```
+src/
+├── cli.ts, server.ts              # Commander.js CLI + Fastify server
+├── add/, data-set/                # Command implementations
+├── core/                          # Published library (see package.json exports)
+│   ├── car/                       # CAR file handling (CARv1 streaming)
+│   ├── payments/                  # Payment setup/status
+│   ├── synapse/                   # SDK initialization patterns
+│   ├── upload/                    # Upload workflows
+│   ├── unixfs/                    # Helia integration, browser/node variants
+│   └── utils/                     # Formatting, constants
+└── common/                        # Internal shared code
+```
+
+**Data flow**: Files → Helia/UnixFS → CAR → Synapse SDK → FOC contracts + Curio → PieceCID + proofs.
+
+## Development
+
+**Setup**: `npm install && npm run build && npm test`
+
+**Scripts**: `npm run build` (tsc), `npm run dev` (tsx watch), `npm test` (lint + typecheck + unit + integration), `npm run lint:fix`
+
+**Requirements**: Node.js 24+, TypeScript ES modules, Biome linting
+
+**Tests**: Vitest (unit + integration), mock SDK at `src/test/mocks/synapse-sdk.js`
+
+## Key Patterns
+
+**Synapse SDK**: Initialize with callbacks (onProviderSelected, onDataSetResolved, onPieceAdded), upload returns {pieceCid, pieceId, provider}. See `src/core/synapse/index.ts`, `src/core/upload/synapse.ts`.
+
+**CAR files**: CARv1 streaming, handle 3 root cases (single/multiple/none), use zero CID for no roots. See `src/core/car/car-blockstore.ts`.
+
+**UnixFS**: Helia for directory imports, chunking, CID calculation. See `src/core/unixfs/`.
+
+**Payments**: `checkPaymentStatus()`, `setupPayments()` in `src/core/payments/index.ts`.
+
+## Biome Linting (Critical)
+
+- **NO** `!` operator → use `?.` or explicit checks
+- **MUST** use `.js` extensions in imports (`import {x} from './y.js'` even for .ts)
+- **NO** semicolons at line end (`semicolons: "asNeeded"`)
+- **MUST** use kebab-case filenames
+
+## Common Pitfalls
+
+1. Import extensions required (`.js` even for .ts files)
+2. Handle 3 CAR root cases (none/single/multiple)
+3. Provider info may be undefined
+4. Clean up CAR files and Helia instances on failure
+5. Browser vs Node variants (check package.json exports)
+
+## CLI & Environment
+
+**Commands**: `payments setup --auto`, `add <file>`, `payments status`, `data-set <id>`, `server`
+
+**Required env**: `PRIVATE_KEY=0x...` (with USDFC tokens)
+
+**Optional**: `RPC_URL` (default: Calibration), `PORT`, `HOST`, `DATABASE_PATH`, `CAR_STORAGE_PATH`, `LOG_LEVEL`
+
+**Default data dirs for pinning server**: Linux `~/.local/share/filecoin-pin/`, macOS `~/Library/Application Support/filecoin-pin/`, Windows `%APPDATA%/filecoin-pin/`
+
+## Git Policy
+
+Conventional commits. Never `git commit` or `git push` without explicit user permission. Ask first, draft message, wait for approval.
+
+## License
+
+Apache-2.0 OR MIT